JP4133798B2 - Wavelength selective photodetector - Google Patents

Description

  The present invention relates to a photodetector, and more particularly to a photodetector capable of selecting a wavelength and having an increased S / N ratio.

  The photodetector is an element that detects an optical signal and converts it into an electrical signal having the same information, and utilizes a pyroelectric effect that enables light detection by changing incident infrared rays into a voltage. There is a detector and a semiconductor detector using carrier generation in a semiconductor by light absorption. Semiconductor photodetectors include diode-type photodetectors and photoconductor-type photodetectors. The semiconductor photodetector is manufactured mainly using silicon and gallium arsenide.

  FIG. 1 is a conceptual diagram schematically showing an avalanche photodetector among semiconductor photodetectors.

Referring to FIG. 1, the conventional avalanche photodetector has a structure in which an i (π) -type light absorption layer 13 and a P-type amplification layer 15 are interposed between a P ⁺ -type semiconductor electrode 11 and an N-type semiconductor electrode 17. Have The P ⁺ -type semiconductor electrode 11 is connected to an external negative electrode, the N-type semiconductor electrode 17 is connected to an external positive electrode, and is driven by applying a strong reverse bias voltage across the photodetector.

  FIG. 2 is a graph showing the electric field strength distribution in the photodetector when a reverse bias voltage is applied. Referring to the drawing, the strongest electric field is applied to the P-type semiconductor amplification layer 15. The electric field affects the mobility of electrons and holes generated in the light absorption layer 13.

FIG. 3 is a conceptual diagram showing the movement of electrons and holes in the avalanche photodetector of FIG. Referring to the drawing, photocarriers injected by a reverse bias voltage absorb light energy in the i (π) -type light absorption layer 13 to form electron-hole pairs, and the formed electron-hole pairs are Accelerated by reverse bias. Holes accelerated to the negative electrode are absorbed by the P ⁺ -type semiconductor electrode 11, but electrons accelerated to the positive electrode sequentially collide with atoms of the P-type semiconductor amplification layer 15 to which a strong electric field is applied, and are secondary. Electrons are generated to amplify the current. This is called an avalanche phenomenon.

FIG. 4 is a circuit diagram schematically showing an equivalent circuit of the conventional avalanche photodetector shown in FIG. As shown in the figure, in the conventional avalanche photodetector, the noise current I _noise component flows through the circuit together with the signal current I _sig .

  The avalanche photodetector can detect a very weak optical signal due to the avalanche phenomenon, and has an advantage that the structure has a small junction capacitance and excellent response characteristics. However, the conventional avalanche photodetector has a thermal noise due to an increase in temperature, that is, a shot noise phenomenon occurs as a large photocurrent having a Johnson-Nyquist noise and a wide bandwidth flows, and a signal-to-noise (S / N) phenomenon occurs. It has the disadvantage that the ratio is degraded. In order to reduce shot noise, it is important to reduce the bandwidth Δf of the reception frequency and the dark current of the photodetector. There is also a need for a solution that compensates for the shortcomings of noise currents due to strong reverse bias voltages acting on the photodetector.

  The technical problem to be solved by the present invention is to provide a photodetector having a structure capable of improving the S / N ratio, in order to improve the above-described problems of the prior art.

  In order to achieve the above object, the present invention provides a transparent upper electrode including a capacitor, a first semiconductor layer located under the upper electrode, and a lower part of the first semiconductor layer, which absorbs light. A light absorbing layer that generates electron and hole pairs, an amplification layer that is located under the light absorption layer and generates secondary electrons, a second semiconductor layer formed under the amplification layer, There is provided a photodetector comprising: a lower electrode including an inductance located under the second semiconductor layer and connected in parallel with an external resistor.

  The capacitor functions as an optical filter in which a plurality of dielectric thin films are stacked between two conductive thin films to transmit light in a specific wavelength band.

  The conductive thin film can be formed of ITO or ZnO.

The dielectric thin film can be formed of SiO ₂ or SiN _x .

  The upper electrode may have a bonding pad attached to the surface in ohmic contact with the external resistor and the external power source.

  The upper electrode is spaced apart from the first circular electrode by a predetermined distance from a central first circular electrode where a bonding pad in ohmic contact with the external power source is located, and a bonding pad in ohmic contact with the external resistor is attached. A second circular electrode; and a circular insulating film positioned between the first and second circular electrodes.

  The lower electrode functions as an inductor in which a coil is spirally formed on an insulating film.

  The lower electrode has a hole formed in ohmic contact with an external element.

The first semiconductor layer may be a P ⁺ type semiconductor, the amplification layer may be a P type semiconductor, and the second semiconductor layer may be an N type semiconductor layer.

  In the present invention, a high frequency noise component can be removed by forming an LC resonance circuit by including a capacitor and an inductor in the upper electrode and the lower electrode. Further, by forming a capacitor by forming a conductive thin film and a dielectric thin film in multiple layers, it is possible to add a function as an optical filter capable of filtering only light in a specific wavelength band.

  The photodetector according to the present invention can increase the S / N ratio by forming a resonant circuit (LC) including an inductor in the upper electrode and an inductor in the upper electrode, and cutting off noise components from the external resistance.

  In addition, the photodetector according to the present invention includes a capacitor that functions as an optical filter by forming a conductive thin film and a dielectric thin film in multiple layers, and can filter light in a specific wavelength band.

  Hereinafter, a photodetector according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 5 is a conceptual diagram schematically showing a photodetector according to an embodiment of the present invention.

  Referring to FIG. 5, the photodetector 30 includes an upper electrode 31, a first semiconductor layer 33, a light absorption layer 35, an amplification layer 37, a second semiconductor layer 39, and a lower electrode 41 in order from the upper side.

  The upper electrode 31 includes a capacitor C formed by laminating a transparent first conductive thin film 31a, a dielectric thin film 31b, and a second conductive thin film 31c. A first circular electrode through which light is transmitted is provided at the center of the upper portion of the first conductive thin film 31a, and a circular insulating film is formed so as to cover the outside of the first circular electrode. A second circular electrode is formed. A bonding pad connected to an external power source may be attached to the first circular electrode, and a bonding pad connected to an external resistor may be attached to the second circular electrode.

The capacitor C can be formed in multiple layers by depositing a plurality of conductive thin films 31a and 31c and a dielectric thin film 31b. The conductive thin film 31a can be formed of a material such as ITO or ZnO, and the dielectric thin film 31b can be formed of a material such as SiO ₂ or SiN _x . If the first and second conductive thin films 31a and 31c are formed of a dielectric material, the capacitor C selects light in a specific wavelength band and serves as an optical filter that exhibits minimum response to light in other wavelength bands. Can function.

  If the first semiconductor layer 33 is a P-type semiconductor, the second semiconductor layer 39 is an N-type semiconductor, the amplification layer 37 interposed between the first and second semiconductor layers 33 and 39 is a P-type semiconductor, and absorbs light. The layer 33 is formed of an N-type semiconductor. If the first semiconductor layer 33 is doped with N-type ions, the second semiconductor layer 39 is doped with P-type ions, the amplification layer 37 is doped with N-type ions, and the light absorption layer 33 is doped with P-type ions.

  The lower electrode 41 functions as an inductor by forming a coil 41b in a spiral shape in the insulating film 41a as shown in FIG. A hole 41c is formed at the center of the lower electrode 41 so as to be in ohmic contact with an external element.

  The upper electrode 31 functions as a capacitor and the lower electrode 41 functions as an inductor, and the photodetector according to the embodiment of the present invention forms an LC resonance circuit as a whole including the upper electrode 31 and the lower electrode 41.

  If a strong reverse bias is applied to the upper electrode 31, the light incident through the upper electrode 31 is absorbed by the light absorption layer 35 via the first semiconductor layer 33 after the high frequency noise component is removed by the capacitor C. The light absorbed by the light absorption layer 35 generates a pair of electrons and holes, the electrons move toward the N-type second semiconductor layer 39, and the holes move to the P-type first semiconductor layer 33. Move towards. The electrons moving toward the second semiconductor layer 39 collide with the atoms of the P-type amplification layer 37 to generate secondary electrons, and thereby the current amplified in proportion to the amount of received light flows through the photodetector. . It extracts as an electrical signal through the lower electrode 41 and detects information of the optical signal.

  FIG. 6 is a simplified circuit diagram of the photodetector shown in FIG. 5 according to the embodiment of the present invention.

  Referring to FIG. 6, the capacitor C, the photodetector structure PD, and the inductor L are connected in series, and the photodetector structure PD, the inductor L, and the external resistor R are connected in parallel. Here, the structure PD of the photodetector includes a first semiconductor layer 33, a light absorption layer 35, an amplification layer 37, and a second semiconductor layer 39 except for the upper electrode 31 and the lower electrode 41 in FIG. Indicates.

The negative electrode of the power supply V to the capacitor C, the positive electrode is connected to the inductor L, the noise current I _n flows through the power supply V, only the signal current I _s flows through the external resistor. The voltage V of the power source of the present invention, the voltage of the inductor L is V _L , the inductive reactance X _L of the inductor L, and the capacitive reactance X _c of the capacitor C have a relationship as shown in Equation 1.

If the capacitor C increases, V _L approaches V, but the noise of the power supply is generally filtered by a reactance X _L inserted as a high-frequency component at a connection portion between the light receiving element and the ground. This is because the circuit impedance increases as the reactance increases due to high frequency components. Accordingly, a photodetector according to an embodiment of the present invention, since only a pure signal current I _s by light flows through the external resistor R, can be designed smaller the value of the external resistor R. In addition, since the inductor L and the capacitor C serve as a band-pass filter, the S / N ratio of the detector can be expressed as Equation 2.

Here, M is a gain, is a shot noise power, is a thermal noise power, and is a signal power. By designing the photodetector according to the embodiment of the present invention to have a circuit structure for detecting a signal in a specific frequency band, the frequency selectivity can be increased. In such a circuit structure, Δf decreases, X _L decreases, and the S / N ratio of the entire photodetector increases.

  Although many items are specifically described in the above description, they do not limit the scope of the invention and should be construed as examples of preferred embodiments.

  For example, those skilled in the art can adopt various structures and arrangements that can increase the performance of capacitors and inductors according to the technical idea of the present invention. Accordingly, the scope of the invention should not be determined by the embodiments described, but by the technical spirit described in the claims.

  The present invention can be applied to a wavelength selective photodetector that functions as an optical filter that can remove high-frequency noise components and filter only light in a specific wavelength band.

It is sectional drawing which shows the conventional avalanche photodetector simply. It is a graph which shows the intensity | strength of an electric field in each thin film layer of the avalanche photodetector of FIG. It is a conceptual diagram which shows a movement of an electron and a hole with the avalanche photodetector of FIG. It is a circuit diagram of the avalanche photodetector of FIG. It is a conceptual diagram of the photodetector by the Example of this invention. FIG. 6 is a circuit diagram of the photodetector in FIG. 5.

Explanation of symbols

30 Photodetector 31 Upper electrode 31a First conductive thin film 31b Dielectric thin film 31c Second conductive thin film 33 First semiconductor layer 35 Light absorbing layer 37 Amplifying layer 39 Second semiconductor layer 41 Lower electrode 41a Insulating film 41b Coil 41c Hole

Claims (11)

A transparent upper electrode including a capacitor;
A first semiconductor layer located below the upper electrode;
A light absorption layer located under the first semiconductor layer and absorbing light to generate electron and hole pairs;
An amplifying layer located under the light absorbing layer and generating secondary electrons;
A second semiconductor layer formed under the amplification layer;
A photodetector, comprising: a lower electrode including an inductance located under the second semiconductor layer and connected in parallel with an external resistor.   The photodetector according to claim 1, wherein the capacitor is an optical filter in which a plurality of dielectric thin films are stacked between two conductive thin films to transmit light in a specific wavelength band.   The photodetector according to claim 2, wherein the conductive thin film is ITO or ZnO. The photodetector according to claim 2, wherein the dielectric thin film is made of SiO ₂ or SiN _x .   The photodetector according to claim 2, wherein the upper electrode has a bonding pad attached in ohmic contact with the external resistor and an external power source. The upper electrode is
A first circular electrode in the center where a bonding pad in ohmic contact with the external power source is located;
A second circular electrode spaced apart from the first circular electrode by a predetermined distance and having a bonding pad attached in ohmic contact with the external resistor;
The photodetector according to claim 5, further comprising a circular insulating film positioned between the first and second circular electrodes.   The photodetector according to claim 1, wherein the lower electrode is an inductor in which a coil is spirally formed in an insulating film.   The photodetector according to claim 7, wherein the lower electrode has a hole formed in ohmic contact with an external element. The photodetector according to claim 1, wherein the first semiconductor layer is a P ⁺ type semiconductor layer.   The photodetector according to claim 1, wherein the amplification layer is formed in a P-type semiconductor layer.   The photodetector according to claim 1, wherein the second semiconductor layer is formed on an N-type semiconductor layer.

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